Cancer Pain: Causes, Types and Assessment

 

SUMMARY

Pain is a common and dreadful symptom in cancer patients, but is often under-treated.  It has a high morbidity if not well controlled.  Cancer pain is mainly of chronic nature which is quite different from acute pain. Success of control depends very much on the accuracy of assessment because the causes are multifactorial including biological, psychosocial, cultural and spiritual.  Causes, type and approach in assessment of cancer pain are discussed.

 

INTRODUCTION

Pain is defined as an unpleasant sensory and emotional experience, associated with actual or potential tissue damage, or described in terms of such damage.¹  It is a common and most dreadful symptom in patients suffering from cancer.  Eighty-eight percent of cancer patients have pain in their last year of life.²  It is a physical suffering which can be modified by physical and psychological factors such as temperature and emotion as well as social and spiritual factors.   The term "total pain" signifies the importance of all these dimensions of a person's suffering, and that good pain relief is unlikely without attention to all these areas.³

 

Half of the patients who have cancer related pain do not receive adequate pain control.²  The main reasons include poor pain assessment, concerns about side effects and development of tolerance in the use of narcotics, as well as a lack of awareness of current knowledge of mechanisms of pain and the modalities of treatment.  Family physician, the primary care provider, is usually the first person being approached by the patient for relief of new pain or deterioration of pain which was formerly well controlled.  Adequate assessment of pain is a critical component for defining the appropriate management plan in patients with cancer pain.

 

CHARACTERISTICS OF CANCER PAIN

Acute pain causes sympathetic hyperactivity with palpitation, hypertension, pupillary changes, sweating and pallor. Cancer related chronic pain is not simply prolonged acute pain.  The patients with chronic pain adapt to it and have few of these symptoms except during exacerbation of pain.  Repeated noxious stimulation in chronic pain leads to a variety of changes within the central nervous system.  Accentuated neuronal responses occur in the dorsal horn of the spinal cord leading to increased and prolonged pain perception.  This, termed 'wind up' and mediated via the excitatory amino acid N-methyl-d-aspartate (NMDA) receptor, has to be prevented by early control of pain to avoid subsequent development of pain that is refractory to treatment. 

 

Chronic pain is devastating and demoralising.  The patient, constantly anxious and reminded of impending death, cannot sleep, becomes worn down and may welcome death.  Relief of pain can restore decision making capacity and enhance the patient’s right to self-determination.

 

CAUSES OF CANCER PAIN

Most pain is caused by cancer itself.  Nineteen percent is due to treatment of cancer and 3% is unrelated to cancer.  Table 1 shows the common causes of pain in cancer patients.  However, the cause of pain in some patients cannot be explained after exhaustive examination and investigation.

 

Table 1: Causes of pain in cancer patients

·  Tissue destruction/metastasis	·  Pressure or distension
·  Trauma / fracture ·  Muscle spasm (back, shoulder, headache) °         often related to anxiety & stress ·  Infection (pelvic cancer or fungating breast cancer)	·  Neurological °         Compression, infiltration °         Generalised neuropathy °         Brain and spinal cord tumour °         Dysaesthetic nerve pain
·  Ischaemia (in tumour or by compression)	·  Tenesmus (spasm in rectal cancer)
·  Depression and anxiety	·  Co-existing pathology such as arthritis
·  Disturbed metabolism (­Ca++ & uraemia) exacerbate existing pain	·  Pain associated with cancer treatment °   Post-chemotherapy pain syndrome °   Postsurgical neuropathic syndromes – post-mastectomy, post-thoracotomy, phantom limb and stump pain °   Post-radiation pain syndrome

 

TYPES OF PAIN

There are three main types of pain: nociceptive, neuropathic and muscle spasm.

 

Nociceptive pain

It has two sub-types, somatic and visceral.   The somatic sub-type arises from skin, myofascial structure and bone.  The visceral sub-type that arises from organ capsule distension causes dull ache while that arising from hollow organ spasm produces colicky pain.  Both kinds of visceral pain may have referred pain presenting far from the origin of pain.  Relatively sparse innervation of the viscera may be one reason why visceral pain is often described in vague terms.  Table 2 shows the causes and symptoms of visceral pain.

 

Table 2: Causes, symptoms and signs of visceral cancer pain

Cause	Symptoms and Signs
·  hollow organ spasm	·  colicky pain, intermittent, griping
·  duct obstruction - ureter, intestine, biliary duct	·  nausea & vomiting ·  palpable enlarged organ ·  increased bowel sounds, jaundice
·  distension of solid organ capsule - liver, kidney	·  dull ache or soreness, ·  "deep", discomfort ·  heavy or pressure sensation ·  organomegaly, may be tender

 

 

Neuropathic pain

Neuropathic pain has two sub-types, central pain and peripheral pain.  The central pain is caused by intracranial or spinal cord malignancy.  Phantom limb pain and postherpetic neuralgia are peripheral neuropathic pain.  The pain caused by stretching, compression, infiltration or injury of peripheral nerves belong to the peripheral subtype.  In reality, neuropathic pain is probably under-diagnosed since many tumours can cause minor nerve trauma by infiltrating smaller cutaneous branches of large nerves.  Most of the post-surgical and post-radiation pain are caused by direct injury of nerves, fibrosis around nerves and neuroma formation of severed nerves.  Radiation for spinal cord compression can cause myelopathy.  Chemotherapy can cause painful neuropathy.

 

Symptoms of neuropathic pain

It can present in different ways:

1.   Abnormal sensation⁴

a.   Dysaesthesia is an abnormal tingling, burning, pins and needles sensation or lacinating, lightning, short sharp shooting pain

b.   Allodynia refers to pain caused by a stimulus that is not normally painful such as light touch.

c.   Hyperalgesia is exaggerated pain caused by a normally painful stimulus.

d.   Hyper/hypoaesthesia is an increased/decreased sensitivity to stimulation.

e.   Hyperpathia is an explosive and often prolonged response to a stimulus.

2.   Phantom limb pain is a kind of deafferentation pain where the pain is felt beyond the site of amputation.

3.   Complex Regional Pain Syndrome with sympathetic nervous instability appears distal to a nerve injury.  It is a combination of       

a.   spontaneous pain, pain on light touch (allodynia) or hyperalgesia.

b.   autonomic dysfunction such as oedema, warmth and sweating with vasodilatation and atrophic changes and

c.   atrophic changes such as thinning of skin, loss of hair and abnormal nail growth.

4.   Central pain

 

Muscular spasm

It can present as tension headache or shoulder girdle muscle pain as a result of constant anxiety and stress.  Spinal column pathologies such as metastases or degeneration can cause muscle spasm in the paravertebral muscles.  The involved muscle may be tender and firmer than normal on feeling.  Pain occurs on stretching it.  The range of movement is reduced by pain in the muscle rather than in the joint.

 

ASSESSMENT

 

A precise diagnosis of the mechanism of pain and classification facilitates the use of correct analgesic techniques and employment of non-pharmaceutical measures.  However, sometimes the pain has to be reduced first without a definite diagnosis to facilitate the necessary assessment.

 

The patient may complain of pain in different parts of the body.  Every pain should be fully assessed.  Assessment is necessary at every visit.  New types of pain may appear and a new kind of treatment needed.

 

History

Because of complaint of multiple symptoms and of pain at multiple sites, some of which cannot be explained by exhaustive assessment, the pain may easily be dismissed as psychological in origin.  A thorough history should be taken from both the patient and carers.

 

Clinical Assessment

Pain is a subjective feeling, not a diagnosis by itself.  Its perception and the patient’s response to it are determined by multiple factors.  Table 3 shows the important questions to be asked in assessment of each site of pain.

 

Table 3: History to be taken about pain.

·        Site and referral of pain ·        Quality and severity of pain ·        Exacerbating and relieving factors ·        Chronology °         onset °         time of day °         duration °         frequency if episodic or intermittent °         breakthrough pain under the current treatment °         relation to medication °         relation to activity ·        Associated symptoms and signs ·        Interference with activities of daily living ·        Emotional impact upon the patient and his fear ·        Significance and meaning to the patient, its perceived cause ·        Patient's expectation of treatment ·        Patient's previous pain experience ·        Response to previous and current analgesic therapies

 

The physical characteristics of the pain can help to identify the cause.  The location and its referral indicate the possible organs responsible.  If the patient can localise pain with one or two fingers to a discreet anatomical site, it is highly likely that the pain is somatic in nature.  A good example would be pain from bone metastases.  Patients typically localise visceral pain badly, with large areas often being indicated with the whole hand or expansive gesture.

 

The quality of pain helps to differentiate between different types of pain.  Ascertain whether it is dull, sharp cutting, paroxysmal shooting, stabbing, lightning, pins & needle, allodynia, burning, heavy, pressure, colicky or constricting.

 

Measurement of Pain

A quantitative measurement with a common descriptive language is useful for monitoring progress. With it, disparities between reported pain and observed distress may become more evident.  It can also facilitate communication between care providers.  

 

Three quantitative methods are commonly used to measure the severity of pain.  There is a high degree of association between them.⁵

 

NUMERICAL RATIO SCALE (NRS)

The patient is asked to rate the pain by choosing a number between 0 and 10 with 0 representing no pain and 10 the worst imaginable pain.⁶  It can be documented by the patient in the record at different times of the day, e.g. 4/10 at 10 p.m. together with the time of taking regular analgesic and analgesic for breakthrough pain.

 

VISUAL ANALOGUE SCALE (VAS)

Ask the patient to assess the severity of pain by marking a position on a line 10 cm long with 0 representing no pain and 10 cm the worst imaginable pain.⁶  It is useful for comparison of the same patient at different points in time.

 

VERBAL DESCRIPTOR SCALE (VDS)

The patient is asked to choose the most appropriate word that can describe the severity of his pain: none, mild, moderate, severe, excruciating.

 

Associated symptoms

Presence of associated symptoms such as fever, dysuria, vomiting and diarrhoea can help in finding the cause of pain.

 

Past history

Past history of cancer treatment can be helpful in the diagnosis of specific syndromes such as post-mastectomy syndrome, post-thoracotomy syndrome and phantom limb.  Any past history of alcohol or drug dependence can affect the use of analgesic in the patient.

 

Co-existing pathology such as duodenal ulcer or concurrent treatment such as the use of warfarin can affect the choice of non-steroidal anti-inflammatory drugs (NASIDs).  The dose or frequency of morphine has to be reduced in patients with renal failure.

 

The response to past and current pain treatment with regards to both effects and side effects matters much in clinical management decisions such as the choice of drugs. 

 

Non-physical factors

Psychosocial, cultural and spiritual factors can affect the perception and description of pain and the rating of its intensity by the patient.⁷ Pain can affect the patient's mood and vice versa.  Is there any anxiety, depression or fear?  What is the patient’s personal meaning of pain such as cause and prognosis?  The thought that pain is proportional to progression or recurrence of the disease may cause immense anxiety and hence profound psychological effect on pain.⁶  Is there any personal, social, interpersonal, family, financial or legal problem or problems related to self-care?⁸ Is there any secondary gain?  Is the patient asking for morphine for more sedation?  Is the pain the patient’s manipulative weapon?  These should be particularly looked for if the pain is refractory to treatment.⁸ The effect of pain on the patient’s life, such as sleep, meal, libido and effect on family is also a good indicator of the severity of pain.

 

The family physician who has had a lasting relationship with the patient understands the coping capability, cultural and spiritual background of the patient and family.  With the trust that has been built over years, the patient and family would more readily disclose their psychosocial problems and feelings to their family physician than the other team members.

 

 

Validated Instruments

There are three commonly used simple, efficient and valid assessment instruments that can provide rapid evaluation in clinical settings of the major physical and psychosocial aspects of pain experienced by cancer patients.  These are also invaluable in evaluating the quality and quantity of pain in research.  Memorial Pain Assessment card is more commonly used clinically.  The other two, although more cumbersome, are more comprehensive and may be used by the specialist for certain patients.

 

MEMORIAL PAIN ASSESSMENT CARD

This simple assessment tool has been proven to be valid, reliable, efficient and sensitive in evaluating individual patients ^9,10 (figure 1).  The card is folded so that only one of the four pages is shown at any one time.  The mood scale, pain scale and relief scale are in the form of visual analogue scales.  The patient can circle the adjective printed randomly on page two that best describes the severity of pain.

 

Figure 1: Memorial Pain Assessment Card

Page 4                                                    Page 2                       

            MOOD SCALE                                                                                                                                                                                                  Mild                             Moderate

                                                                 Just noticeable             Strong 

Worst                                       Best            Severe                       Excruciating

 mood                                      mood      No pain                        Weak

                                                                                                

             PAIN SCALE                                          RELIEF SCALE

Least                                        Worst      No                                        Complete

possible                                  possible    relief                                          relief

pain                                          pain        of pain                                    of pain

 

Page 1                                                    Page 3

 

WISCONSIN BRIEF PAIN INVENTORY

It addresses the history, intensity, location and quality of pain.  It also addresses pain's ability to interfere with the patient's activities and helps to provide an understanding of its cause.  The patient is also asked to report the medication or treatment they received for pain, the effect of treatment and their belief about the cause of pain.¹¹

 

Many of its questions are in the form of numerical rating scales or multiple-choice questions.  It has been translated into several languages.  Patients from widely different cultural and linguistic backgrounds respond to rating in a similar fashion.^11,12

 

McGILL PAIN QUESTIONNAIRE

It is a questionnaire designed to answer four questions:

1. Where is your pain?

2. What does it feel like?

3. How does it change with time?

4. How strong is it?

 

For each question, there are many multiple-choice sub-questions.  Altogether, there are 78 adjectives in 20 categories that describe sensory, affective and evaluative components of current pain.^11,13  It is a reliable multi-dimensional measure of immediate pain.  However, it may be difficult and cumbersome for patients to understand and complete.  It can also be limited by its language constraints, wherein patients of non-English speaking background may find it difficult to answer.¹¹

 

Physical Examination

There is no direct correlation between pain and visible or observable signs.  Patients with chronic pain do not become sweaty or hypotensive.  Observation of the patient's level of activity may give an indication of the degree of disability caused by the pain. In unconscious patients, frowning, posture change, general increase in muscle tone, restlessness, grimacing, any pupillary dilatation, increased sweating, tachypnoea or tachycardia may indicate the presence of pain.

Medical Examination

Inspect and palpate the site of each pain.  Look out for enlarged organs such as liver, kidney from obstructed ureter, lymph nodes or distended bladder.  Feel for muscle spasm.  Examine the fundi and do a rectal examination.

Neurological Examination

Neurological examination often allows some anatomical localisation of the cause, especially when there is involvement of the spinal cord or nerve roots.  Check for the degree of motor and sensory change, reflex, gait, posture, cranial nerve signs, cerebellar signs as well as urinary and anal sphincter functions.  The distribution of abnormal signs may correlate with dermatomes and in turn spinal segments.⁶

 

 

Investigation

Investigation is seldom indicated.  Sometimes it is necessary to answer a specific question, to clarify a diagnosis, to aid the comparison of the benefits and risks of therapeutic intervention. Decision on whether to do the investigation depends on the life expectancy and level of function of the patient, the adverse effect on the patient’s quality of life, his ability to participate in the procedure, the patient’s and family’s willingness to participate.  The patient’s and family’s decision must be respected.

 

The commonest blood tests for pain are erythrocyte sedimentary rate (ESR), liver and renal functions as well as electrolytes especially corrected calcium.  A raised ESR may be an indication of a paraneoplastic syndrome.  Hypercalcaemia may exacerbate pain by increasing neuronal depolarisation and is a treatable cause of pain.  Impaired liver function may indicate presence of hepatic secondaries and means that opioid effects will last longer.  Raised creatinine may be caused by an obstructed urinary system, so that opioids have to be given in lower dosage and less frequently.  NSAIDs can worsen the kidney condition.

 

Imaging techniques are useful in revealing anatomical lesions.  Plain abdominal X-ray is sometimes used to assess the severity of faecal impaction and for confirmation of intestinal obstruction.   Bone scan helps in detecting bone secondaries but is not specific. CT scan is more sensitive and specific than either plain x-ray or bone scan in distinguishing benign from malignant vertebral diseases.  It is good for identifying paravertebral mass but it does not accurately assess when a tumour has extended into epidural space.  MRI is ideally the investigation of choice for spinal cord compression.

 

RE-ASSESSMENT

As cancer is a progressive disease, new or more extensive pain can be anticipated.  Repeated reviews of pain are essential.  Pain not responding to therapy may indicate the diagnosis is incorrect or that other factors, such as depression, coexist and need treatment.  Pain which was well controlled and then worsens may be due to progression of the disease or a new cause begins to occur rather than development of pharmacological tolerance to morphine.¹⁴  The extent of cancer needs to be re-evaluated and a thorough assessment needs to be repeated.  Cancer pain can be controlled in 80% of patients.  If it is not controlled within a week, consider specialist advice.⁴

 

REFERENCES

1.    WHO. International Association for the Study of Pain, 1979.

2.    Addington-Hall J, McCarthy M. Dying from cancer; results of a national population-based investigation. Palliat Med, 1995; 9(4):295-305.

3.        Saunders CM, The Management of Terminal Illness, London: Hospital Medicine Publication, 1967.

4.    Faull C, Carteer Y, Woof R. Handbook of Palliative Care, Blackwell Science Ltd: Oxford, 1998:103-8.

5.    De Conno F, Caraceni A, Gamba A, et al, Pain measurement in cancer patients: a comparison of six methods, Pain 1994; 57(2):161-6.

6.     Woodruff R. Cancer Pain, 2nd edition, Asperula Pty Ltd: Melbourne, 1999: 18-23.

7.     Rudy TE, Kerns RD, Turk DC.  Chronic pain and depression: toward a cognitive-behavioural mediation model. Pain, 1988; 35:129-140.

8.        Woodruff R. Palliative Medicine, 2nd edition, Asperula Pty Ltd: Melbourne, 1996; 50-3.

9.     Swllenstein SL. Measurement of pain and analgesia in cancer pain. Cancer, 1984; 53:2217-384

10.  Fisherman B. The Memorial Pain Assessment Care: A valid instrument for the evaluation of cancer pain. Cancer, 1987; 60:1151-8.

11.  Doyle D, Hanks GWC, MacDonald N. The Oxford Textbook of Palliative Medicine, 2nd edition, Oxford University Press: New York, 1993: 148-166

12.  Cleeland CS. Demonstration projects for cancer pain relief.  In: Foley KM, Bonica JJ, Ventafridda V, eds. Advances in Pain Research and Therapy. Vol 16. Second International Congress on Cancer Pain.  New York: Raven Press, 1990:465-74.

13.  Graham C, Bond SS, Gerkovich MM, Cook MR. Use of the McGill Pain Questionnaire in the assessment of cancer pain: replicability and consistency.  Pain, 1980: 8:377-87.

14.  Collin E, Poulain P, Gauvain-Piquard A, et al, Is disease progression the main factor in morphine 'tolerance' in cancer pain treatment? Pain, 1993; 55(3):319-26.

 

KEY MESSAGES

1.        Cancer pain should be treated as ‘total pain’ with contributions from psychological, social, cultural and spiritual factors.

2.        Every pain should be assessed and reassessed from time to time according to biopsychosocial condition of the patient. History has also to be taken from the carers.

3.        A precise diagnosis of the mechanism of pain and classification facilitates the use of correct analgesic techniques and employment of non-pharmaceutical measures.

4.        A quantitative measurement with a common descriptive language is useful for monitoring progress and communication between different professionals.

5.    Pain which was well controlled and becomes worsening may be due to progression of the disease or a new cause begins to occur rather than development of pharmacological tolerance to morphine.